In this paper, the kinematics of vanes is studied with respect to the variable displacement vane pumps. Frictional torques of the vanes, contact forces of vanes on the cam ring and so on are calculated.
The results of calculation and experiment indicate that, in the seal range, the vanes are apt to float on the innerface of the ring owing to excessive pressure increase.
The calculated values of torque due to friction between vane tips and the ring, which account for a large part of the total torque loss, agree fairly well with experimental values. The constituents of the total torque loss are estimated from the foregoing results.

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Torque characteristics of a low-weed high-torque radial piston motor at starting and in the low-weed range were investigated experimentally using an apparatus with a worm gear mechanism.
At first, change of the frictional torque with decrease of rotational speed was measured. And it became clear that the frictional torque increased steeply with the decrease of rotational speed in the very low-speed range less than one rpm.
Next, the starting torque was measured after the test motor was stopped under loading condition for a certain time. Then it became clear that the frictional torque at starting increased with the stopping time.
Finally, the process of disappearing of the frictional torque which was developed during the stopping time was measured after the test motor started. And the process of building up the frictional torque when the inlet pressure of test motor was given was also investigated experimentally.

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Hydraulic servo systems have been used widely in high-speed servo systems so far. Designing a hydraulic system, its dynamic characteristics has been considered seriously, on the other hand, the power efficiency of the system including the power source has been poorly considered.
The purpose of this research is to reduce the fluid power generated in the hydraulic power source as small as possible for saving energy without making its dynamic characteristics worse.
A kind of adaptive systems in which the displacement of the hydraulic motor as the actuator of the system is changed automatically responding to load condition has been newly manufactured for this purpose and the dynamic characteristics including stability of this variable parameter system have been investigated theoretically and experimentally.
As a result, it was clarified that a certain value of delay in displacement switching is necessary in order to decrease the influence of the: witching on the stability of the system.

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